III-V semiconductor materials, such as, for example, III-arsenides (e.g., Indium Gallium Arsenide(InGaAs)), III-phosphides (e.g., Indium Gallium Phosphide (InGaP)) and III-nitrides (e.g., Indium Gallium Nitride (InGaN)), may be employed in a number of electronic device structures, such as, for example, switching structures (e.g., transistors, etc.), light emitting structures (e.g., laser diodes, light emitting diodes, etc.), light receiving structures (e.g., waveguides, splitters, mixers, photodiodes, solar cells, solar subcells, etc.), and/or microelectromechanical system structures (e.g., accelerometers, pressure sensors, etc.). Such electronic device structures containing III-V semiconductor materials may be used in a wide variety of applications. For example, such device structures are often used to produce radiation (e.g., visible light) at one or more of various wavelengths. The light emitted by such structures may be utilized not only for illumination applications, but may also be used in, for example, media storage and retrieval applications, printing applications, spectroscopy applications, biological agent detection applications, and image projection applications.
As a non-limiting example, for the case of InGaN (a III-nitride material), InGaN layers may be deposited heteroepitaxially on an underlying substrate, which may have a crystal lattice that does not match that of the overlying InGaN layer. For example, InGaN layers may be deposited on a semiconductor substrate comprising gallium nitride (GaN). The GaN may have a relaxed (i.e., substantially strain free) in-plane lattice parameter of approximately 3.189 Å, and the InGaN layers may have a relaxed in-plane lattice parameter, depending on the corresponding percentage indium content, of approximately 3.21 Å (for 7% indium, i.e., In0.07Ga0.93N), approximately 3.24 Å (for 15% indium, i.e., In0.15Ga0.85N), and approximately 3.26 Å (for 25% indium, i.e., In0.25Ga0.75N).
In greater detail, the InGaN layer may initially grow “pseudomorphically” to the underlying substrate, such that a lattice parameter of the InGaN layer is caused (e.g., forced by atomic forces) to substantially match a lattice parameter of the underlying substrate upon which it is grown. The lattice mismatch between the InGaN layer and the underling substrate (e.g., GaN) may induce strain in the crystal lattice of the InGaN layer, and this induced strain may increase with increasing thickness of the InGaN layer. As the thickness of the InGaN layer increases with continued growth thereof, the strain in the InGaN layer may increase until, at a thickness commonly referred to as the “critical thickness,” the InGaN layer may no longer grow in a pseudomorphic manner and may undergo strain relaxation. Strain relaxation in the InGaN layer may result in a deterioration of quality in the crystal lattice of the InGaN layer. For example, such deterioration in crystal quality in the InGaN layer may include the formation of crystalline defects (e.g., dislocations), a roughening of an InGaN layer surface, and/or the formation of regions of inhomogeneous material composition.
In addition, upon the onset of strain relaxation, the InGaN layer may incorporate an increased amount of indium. In other words, under constant growth conditions, the percentage of indium incorporated into the InGaN layer at the growth surface thereof may increase, resulting in a non-uniform concentration of indium in the InGaN layer across the thickness thereof. In addition, an increase in indium concentration in the InGaN layer may promote the onset of additional strain relaxation, which may result in a further deterioration in crystal quality of the InGaN layer.